Last week's outbreak of violence, including suicide bombings, has shaken Uzbekistan, raising fears that Islamic militancy has again raised its head in the central Asian nation. It also raises concerns about a repressive reaction by an authoritarian government.

The recent wave of attacks that claimed more than 40 lives is the most severe violence to hit Uzbekistan in five years. Whether the attacks were carried out by the same group that struck in 1999 or were executed by some unknown group is not clear.

The Islamic Movement of Uzbekistan, the IMU, carried out the 1999 bombings, but analysts believed the group had been all but wiped out when its fighters sided with the Taleban and al-Qaida in the fighting in Afghanistan in 2001. IMU military chief Juma Namangani is reported to have been killed in the U.S. bombing there.

Frederick Starr, chairman of the Central Asia-Caucasus Institute at Johns Hopkins University, believes the IMU was decimated and could not have carried out the recent attacks. He thinks they were the work of angry families whose relatives have been jailed and tortured by the government of President Islam Karimov.

"It is a combination of family members of radical Islamists who have been jailed or who have died, and they (were) organized by some folks from without, probably from Afghanistan or Pakistan, in other words, the insider-outsider deal as occurred in Spain," said Mr. Starr. "And I think its main purpose was probably to settle some grudges with the police."

But other analysts believe the attacks were launched by a radical Islamic group born from the ashes of the IMU. Tamara Makarenko is a Central Asia expert at the Center for the Study of Terrorism and Political Violence at the University of St. Andrews in Scotland. She believes many former Islamic fighters drifted back together after the Taleban were toppled from power in neighboring Afghanistan, forming the nucleus of a new group.

"There were a number of remnants, mujahedin, around, whether they were al-Qaida remnants, or whether they are Taleban remnants, or just sort of members of Pakistani extremist groups as well in the area," she said. "You essentially had an influx of mujahedin, if that is what you want to call them, or radical militants, looking for another cause to attach themselves to."

President Karimov sided squarely with the United States and the anti-Taleban forces in the anti-terrorist war, allowing U.S. bases into the country. But one obstacle to improving relations with the United States is that Uzebekistan has a poor balance sheet on human rights. Ms. Makarenko says Mr. Karimov is trying to use his new relationship as an anti-terrorist ally to give political cover to his own hardline rule.

"Karimov, I think, played on this relationship to legitimize the heavy-handed reactions he used internally against what he called radical Islamic opponents," Ms. Makarenko added. "This had an adverse impact on essentially the security of Uzbekistan because it continued to feed into the frustration of really regular people on the ground who were seeking to engage in opposition. And some of that just happened to have an Islamic bent on it."

Human-rights groups estimate that about seven thousand people have been imprisoned in Uzbekistan for religious or political beliefs. The State Department's most recent human-rights report, issued in February, describes Uzbekistan's human-rights record as very poor.

Some analysts believe the attacks were timed to both embarrass Mr. Karimov and prod him into an overreaction against political opponents at a sensitive moment. The State Department must certify this month that Uzbekistan has made significant progress in human rights, and the European Bank for Reconstruction and Development is to decide this week if the Karimov government meets human-rights criteria for new lending. Millions of dollars in aid and loans hang in the balance of those decisions.